Whipped Icing?

I am making an airplane cake for my nephew's 1st birthday in 2 weeks and was wondering what kind of icing would be best for doing puffy clouds. Could someone please point in the right direction? Thanks your your time and help.

I did clouds on my cake a couple weeks ago. I just used white butter cream and piped groups of large dots to give the look of puffy clouds. I thought it turned out okay, but it was my first try. You can see it in my pictures. Hope this helps some, but I would love to hear other responses.